1. Field of the Invention
The present invention relates to a method for coating a COB(Chip On Board) type semiconductor package, and more particularly, to a method for fabricating a COB type semiconductor package, which is suitable for simplifying a process from wire bonding to milling.
2. Discussion of the Related Art
In general, semiconductor packages are either a hole inserting type or a surface mounting type. In the hole inserting type package, there are holes in a printed circuit board for inserting and soldering leads or pins thereto. On the other hand, in the surface mounting type package, inserting holes are not required, and ICs are mounted on a surface of a printed circuit board. This surface mounting type package allows mounting of the ICs on both sides of the printed circuit board leading to a significant improvement of an IC density mounted on the printed circuit board, enabling a package that is lighter, thinner, shorter and smaller to be obtained. Currently, surface mounting type packages come in subtypes of SOP(Small Outline Package), TSOP(Thin Small Outline Package), SOJ(Small Outline J-bend), and TQFP(Thin Quad Flat Package).
In general, a semiconductor package is fabricated according to the steps, including die sawing to separate a wafer into individual chips, die attaching to connect bond each of the chips separated into individual devices on a lead frame with conductive epoxy, wire bonding for connecting the chip bonded on the lead frame to leads on the lead frame with gold wire, molding to encapsulate the chip having the Ye bonding completed for protecting the chip against external impact, and soldering for dipping ends of outer leads into molten solder to coat with solder to improve a conductivity, trimming and forming.
In addition, a COB(Chip-On-Board) package technology is suitable for reducing cost of the COC(Chip-On-Chip) solution, and include the steps of die bonding to bond chips on epoxy coated on bonding positions of a COB film, conducting a die bond baking to fix to the die(chip) bonded on the COB with epoxy, wire bonding to electrically connect the die bonded on the COB film to external terminals, and coating gold wire used in the wire bonding and chip to protect from external impact. There may also be a milling step to adjust a thickness of the chip as specified in the order.
A background art method for fabricating a COB type semiconductor package will be explained with reference to the attached drawings. FIG. 1A illustrates a plan view showing placing chips on a COB film and conducting wire bonding.
The background art COB type semiconductor package is provided with a COB film 1 having a plurality of bond holes 3 formed therein, chips 2 mounted on the COB film 1, gold wires 4 for connecting the chips 2 to the COB film through the bond holes 3. The COB film 1 is provided with an epoxy layer of a base layer, a capacitor layer, an adhesive layer between the capacitor layer and the epoxy layer, a nickel layer under the capacitor layer, and a plating layer under the nickel layer. That is, the major feature of the COB type package is that chips 2 are directly bonded on the COB film. After connecting the chips 2 and the COB film 1 through the bond holes 3 with gold wires 4, a molding process is conducted for protecting the chips 1. This molding process may be called a coating process.
FIGS. 1B and 1C illustrate sections showing the coating process of the background art semiconductor package.
Referring to FIG. 1B, after bonding chips 2 on the COB film 1, the chips 2 and the COB film 1 are electrically connected with gold wires 4. In the connection, the chips 2 are connected to inner portions of the COB film 1 through the bond holes 3. Liquid resin 6 is applied to the chip 2 through a nozzle 5, for protecting exposed chips 2 and gold wires 4, which can break from a minor impact. As shown in FIG. 1C, after completion of liquid resin coating of the chips 2 and the gold wires 4, the liquid resin is cured to form a solid state body 8. Then, the body 8 is milled as the order specified using a cutting head 7.
However, the background art method for fabricating the COB semiconductor package has the following problems.
First, there may be a gap between the chip and the COB film caused by a defective die bonding process, bonding the chips on the COB film, which forms an inner void that degrades the reliability of the coating process.
Second, expensive coating equipments for coating the resin and complicated robot arms for adjusting coated resin are required, resulting in a complicated fabrication process.
Third, the milling process, required by an order specification increases production cost.
Fourth, precise control of liquid resin deposition is sometimes difficult due to the nozzle being blocked or contaminated while applying the liquid resin.
Fifth, the temperature control of a heater provided around the nozzle must be constantly monitored because the nozzle is very sensitive to a temperature changes.
Sixth, turn around time is long due to the long curing time required to cure the liquid resin.
Seventh, gases and foreign matters may be trapped when filling the liquid resin from a supply container to a storage tank. This may cause the nozzle to operate incorrectly.
Eighth, the liquid resin may only be stored 6 months or less.